Portable terminals, such as smart phones or tablets that are recently, widely used externally include LEDs and cameras for imaging external subjects. Users perform imaging without illumination or in the case where illumination is needed, they allow the LEDs to be turned on and then perform imaging. Thus, the camera and LED are disposed in proximity to one surface of the portable terminal.
Recently, a camera for a smart phone provides resolution similar to a digital camera for a general specialist. Thus, various devices using a smart phone camera are emerging and one of them is a microscope, which captures a magnified image of an object by using a lens additionally installed at the smart phone camera.
A general microscope is designed in a structure that includes an ocular lens and an object lens in opposite ends of a single body tube. The object lens facing a subject is a lens having an extremely short focal length and makes a magnified real image of an object, and the ocular lens facing a user's eyes is a magnifying lens that sees it. A magnification of the microscope may be found by the multiplying of a magnification of the object lens and a magnification of the ocular lens.
A camera that is installed by default in a smart phone generally includes an auto focus (AF) function to change a focal length by minutely changing the distance between an internal lens and an image sensor. At this point, a minimum focal length is set for each camera internal to the smart phone, and a shortest object distance is set according to the minimum focal length. If a subject is located within the shortest object distance, it is difficult to perform imaging or an unclear image may be obtained because the camera is out of focus. Thus, in order to use the smart phone camera as the microscope or the magnifying lens, there is a need for a measure, such as adding a separate object and ocular lens external to the camera to change the focal length and magnify in a certain proportion.
For these purposes, research and development in a type of an optical device that is installed in an internal camera of a smart phone has also been performed in the past. For example, there are a Lupe (magnifying lens) type macro lens and a type of a microscope.
The microscope type includes an object lens and an ocular lens in a body tube like an actual microscope, and a smart phone camera is installed at an ocular lens to be used to produce a digital image. These products are much greater than smart phones, so it is a more accurate expression that the smart phone is installed at such a product and it is difficult to carry it accordingly. With an increase in magnification, the length of a body tube gets longer. For example, Korean Patent No. 1591902 or 1550682 relates to a cradle for holding a smart phone on a microscope and is invention similar to this kind.
The Lupe type macro lens is smaller than the microscope type in volume but has a smaller magnification, and is significantly affected by ambient light because it uses external light. For example, in a backlight state in which illumination is behind a subject, an image of a subject may not be correctly formed because too much light enters a camera, and in the case where surroundings are too dark, it may be difficult to perform imaging because of a lack of lighting.
In the case of the Lupe type, there is also a need to adjust a lens magnification to focus on a nearby object, but in order to obtain a clear image, there is a need to illuminate the object with sufficient light in a state in which external light is blocked. Since it is difficult to solve such a limitation due to the reason that such a fundamental solution affects the pricing of a product, a typical Lupe type lens have no choice but to abandon a clear image instead of securing an amount of light by using external light as it is.
As such, typical devices that have been installed at a smart phone to function as the microscope or magnifying lens are too large and it is uneasy to carry them, or even when it is easy to carry them, there were many types of devices that have instable performance by external light.